FIG. 1a shows a typical networking hardware system 100a with its cover removed. The system 100a (also called a machine or switch or box) typically comprises a power supply 101, a cooling element (such as a fan not shown in FIG. 1), a backplane 103, card interfaces 104a-e attached to backplane 103 and various cards 105a-e inserted into the card interfaces 104a-e. In networking hardware applications the cards are typically organized into three categories: adapter cards (e.g., adapter cards 105a-c), switch or routing cards (e.g., switch or routing card 105d), and processor cards (e.g., processor card 105e).
Usually, most of the cards 105 plugged into a working networking switch (or router) are adapter cards 105a-c. Adapter cards 105a-c are typically used as an interface between the network(s) the switch 100b is connected to and the switch card 105d. The switch card 105d is responsible for collecting all incoming traffic from the adapter cards 105a-c and redirecting the traffic to its appropriate adapter cards 105a-c for outbound traffic flow. The processor card 105e typically has a processing core (e.g., a microprocessor) used to execute the machine's maintenance/configuration software. Although FIG. 1a shows a box 100a,b having only one switch card 105d and processing card 105e, it is possible to have more than one of each of these. Multiple switch cards 105d may be employed to expand system bandwidth and/or provide redundancy. Multiple processing cards 105e may be used for redundancy as well.
All these cards communicate with one another via the backplane 103. The cards are typically connected to the backplane via a card interface 104 which may provide mechanical support for the card as well as electrical connection between the card and the backplane 103. The backplane 103 typically comprises conductive traces (also referred to as nets or wiring) between specific input/outputs associated with each of the card interfaces 104a-e. Thus the backplane 103 is an important and necessary feature of not only a machine's mechanical design but also a its electrical design.
As a networking machine 100 becomes more complex so does the sophistication of the backplane 103. For example, high bandwidth machines (i.e., high end leading edge equipment) typically have multiple switch cards 105b (in order to maximize system bandwidth) each of which require communication with most if not all adapter card interfaces 104a-c. As high bandwidth machines can support more adapter card traffic than lower end machines, such high end machines also have larger banks of adapter cards (as compared to lower bandwidth machines). Properly interconnecting all the various card slots typically requires the backplane to be implemented with multiple (e.g., 20, 22 or more) metal layer electrical cards. Furthermore, the input/output count (i.e., the number of available input/outputs per card interface 104) significantly expands as well.
Because backplanes 103 can be complicated, it is difficult to implement a standard backplane platform. That is, different high end machines require custom backplane designs unique to (and usable only with) one machine. As such, it is difficult to implement a single backplane design that is workable with a number of different machines.
Having the same backplane across varied product lines reduces both development and manufacturing costs substantially. One area of product lines where a common platform is needed concerns SONET (Synchronous Optical NETwork) switch products and ATM (Asynchronous Transfer Mode) switch products. These products may be referred to not only as SONET or ATM switches respectively; but also as machines, systems, or boxes.
SONET switches are used as physical layer extensions. That is, using the B-ISDN ATM reference model, SONET switches do not typically execute networking level functions beyond the physical layer. ATM switches, on the other hand, provide full networking capability which extends their functionality into the AAL layer. As such, the switch cards of the ATM machine tend to be more complex and sophisticated as compared to the SONET machine switch cards.
Nevertheless, there is some commonality between the two machines. Specifically, since ATM frequently uses SONET as a physical layer technology, there tends to be design overlap among ATM switch adapter cards and SONET switch adapter cards. For example, the front end fiber optics and supporting chipsets will tend to be identical (or nearly so) when the adapter cards from the two machines are compared.
Referring to FIG. 1a, a backplane 103 is an electrical card (also referred to ask a PC board or planar board) having card interfaces 104a-e and conductive traces (also referred to as nets or lines or traces or wiring). The backplane is typically comprised of multiple layers of conductive material, each separated from the other by dielectric. The conductive layers are typically formed into individual traces by a lithographic patterning process that employs masks. Mask sets are used to project images of the specific conducting trace patterns associated with each metal layer in a PC board.
PC boards are typically manufactured by forming a conductive layer, patterning the conductive layer (usually with a lithographic process that employs a mask set), forming a dielectric layer over the conductive layer and then repeating the above while also forming contacts through the dielectric to a trace below where needed. Such a process is an example of a manufacturing process. For backplane manufacturing, the manufacturing process may also include affixing card interfaces to the PC board.
FIG. 1B shows a partial schematic of the backplane 103 of FIG. 1A. It is important to note that typically more than one trace exists between cards. Furthermore, other backplane connections such as power and ground, and their associated input/outputs are not shown in FIG. 1B for simplicity. Referring to FIG. 1B, the conductive traces 120a-n within the backplane 103 are used to carry electrical signals between specific input/outputs 121a-n associated with each of the card interfaces 104a-e. input/outputs are any conductive material associated with a card interface 104a-e used to make electrical contact to a card 105a-e (such as metal pins, edges, or sockets). Since the direction of information flow through a specific input/output is up to the designer (i.e., may be either into the backplane 103 or out of the backplane, 103), input/outputs may be used either as inputs or outputs.
Input/outputs are typically housed within a card interface 104a-e such that they face their respective card 105a-e (as opposed to the backplane 103). Each input/output is usually electrically coupled to a specific backplane 103 net 120a-n via the card interface 104a-e itself. Thus, an electrical connection to an input/output corresponds to an electrical connection to its associated backplane 103 net as well (e.g., input/output 121a and net 120a). Furthermore, multiple input/outputs typically reside in a card interface 104. Each card 105a-e is designed such that card nets 124a-n that “mate with” the card interface 104a-e make electrical connection with the input/outputs 121a-n. In this manner, electrical connection between card nets 124a-n and backplane nets 120a-n is realized (e.g. input/outputs 121a, net 120a and net 124a).
Thus, card interfaces 104a-e are used to connect cards to a backplane. They typically provide mechanical support as well as electrical connection between the card 105a-e and the backplane 103. An example of a card interface 104a-e is a connector (frequently made of plastic with copper pins) that is soldered to the backplane PC board. Cards 105a-e are typically “plugged into” card connectors and make electrical connection to the backplane signal traces 120a-n via the input/outputs 121a-n. 
Thus the input/outputs 121a-n may be viewed as a physical translation between card nets 124a-n and backplane nets 120a-n. In order for cards 105 to properly communicate with one another, backplane nets 120a-n should be properly connected at both ends (or more if applicable) to their associated card 124a-n nets (e.g., card net 124a, input/output 121a, backplane net 120a, input/output 121a2 and card net 124a2).
For example, a clock driver net on one card should be connected to a backplane net that is also connected to a clock receiver net on another card. As backplane nets should be “tracked” as to their specific, corresponding card net; input/outputs should similarly be tracked since they are the translation between the two nets. That is, continuing with the former example, a clock driver input/output should mate (or otherwise connect) to a clock driver net on its associated card and a clock receiver input/output should mate with a clock receiver net on its associated card.
Other examples are as follows: power supply card nets should mate with power supply input/outputs, ground plane card nets should mate with ground plane input/outputs, specific data signal nets on a card should mate with their corresponding data signal input/outputs, etc. The multitude of various input/outputs are arranged in the card interface such that each “lines up” and makes electrical contact with its associated card net. Therefore, card interfaces have an arrangement of input/outputs that functionally mate to its corresponding card.
As discussed ahead, one aspect concerns the ability of the backplane to functionally mate one arrangement of input/outputs to two different cards. For example, the same arrangement of input/outputs are designed to functionally mate to both an ATM switch card and a SONET switch card. It may therefore be alternately said, that the backplane has an arrangement of ATM switch card input/outputs in a card interface and an arrangement of SONET switch card input/outputs in the same card interface where the ATM switch card input/outputs and the SONET switch card input/outputs are the same input/outputs. The same may be said for backplane input/outputs designed to mate to adapter cards as well.
Also, the card 105a-e itself may have a backplane connector (not shown in FIG. 1B) that plugs into or otherwise mates to the card interface 104a-e. Such a connector typically has its own input/outputs (connected to the card nets 124a-n) that mate to the card interface input/outputs 121a-n. 